Common indicators and clinical application of syphilis screening

Common indicators of syphilis screening

Syphilis is called a "simulation master" by dermatologists due to the diversity of clinical manifestations. At present, the diagnosis of syphilis is mainly determined by serological tests due to the lack of popular equipment such as dark field or fluorescence microscope. The test methods are divided into two categories due to different antigen preparation methods:

1. Non-Treponema pallidum antigen test, including: (1) Non-Treponema pallidum serum test The antigens of this type of test are divided into cardiolipin, lecithin and cholesterol suspension, which are used to detect anticardiolipin antibodies. Since these tests have the same standardized antigen, the sensitivity is similar. There are three commonly used: ① the venereal disease research laboratory slide test (VDRL); ② serum unheated reagin slide test (USR); ③ rapid plasma reagin ring card test (RPR). It can be used for clinical screening and can be quantitatively used for curative effect observation.

2. Treponema pallidum antigen test, including: ① Fluorescent Treponema pallidum antibody absorption test (FTA-ABS); ② Treponema pallidum hemagglutination test (TPHA); ③ Treponema pallidum brake test (TPI), etc. These tests are highly specific and are mainly used for diagnostic tests.

In the primary screening test, VDRL is not carried out in most hospitals due to the troublesome operation. USR and RPR are improved experimental methods based on VDRL. The operation is simple and the results can be judged with the naked eye. They have the same specificity and sensitivity, so they are widely used. .

In the confirmation test, TPHA and TPPA are widely carried out because of their simple operation, specificity and sensitivity better than FTA-ABS. Generally speaking, excluding the cause of false positives and confirming the anti-IgG Treponema pallidum antibody in the test, even if the treatment is sufficiently standardized, the result can still be positive, so it should not be used as the basis for curative effect observation, recurrence and re-treatment.

False positives and false negatives are "common"

Due to technical reasons, both types of syphilis serological tests have biological false-positive and false-negative problems. Such as: systemic lupus erythematosus, rheumatic heart disease, arthritis, liver cirrhosis, colon cancer, intravenous drug use, pregnancy, diabetes, rubella, filariasis, tuberculosis and other acute and chronic infectious diseases can lead to false positives. Such false positive results have a very low titer after doubling dilution, generally below 1:8, which can be clarified by combining the two types of tests. Due to test sensitivity, prozone phenomenon (high serum concentration of Treponema pallidum antibody inhibits antigen-antibody agglutination), and the length of syphilis infection can lead to false negative test results, such as: RPR positive rates for primary and tertiary syphilis are respectively 85%, 80%. False positives and false negatives can be ruled out in combination with clinical data and re-examination.

How to view the inspection results

When we look at the test results of the syphilis test, we should combine the preliminary screening test, the confirmation test and the comprehensive analysis of the clinical and epidemiological data of the patient. In general, patients with positive RPR and USR tests in the primary screening test and negative confirmation tests exclude infection. If the confirmation test is positive for TPI or TPHA, but the initial screening test is negative, it is considered to be a false positive or the syphilis infection has been cured (a few patients can be cured without treatment). Patients with syphilis are required to be followed up for 2 years after standard treatment. The non-Treponema pallidum test is reviewed every 3 months in the first year, and every six months in the second year. , can be considered to be serofixed and clinically cured. If the titer rises in the follow-up review, it is considered to be recurrence or reinfection, and consultation or treatment with a specialist is required.